Tapu Koko @ Light Clay
Ability: Electric Surge
Nature: Jolly
Tera Type: Flying
EVS: 248 HP 252 SPE 8 DEF
Light Screen
Reflect
U-Turn
Taunt
Tapu Koko is my lead 99% of the time. It can set up screens to allow Garchomp and Mega-Gyarados to set up safely, and ko the opponents. Taunt is needed to stop set-up sweepers like Volcarona, Dragonite, other Mega-Gyarados, Swords Dance garchomp, and many others. U turn is to pivot into those sweepers. Electric surge is helpful for Iron Valiant and Iron Moth as well as prevent sleep, if needed.
Garchomp @ Rockium Z
Ability: Rough Skin
Tera Type: Steel OR Fire
Nature: Jolly (yes there are lots of Jollys but it's a hyper offense team what did you expect?)
EVs: 252 ATK 252 SPE, 4 SPD
Stone Edge
Stealth Rock
Swords Dance
Earthquake
Garchomp is the setup/wall breaker of the team, alongside Mega-Gyarados. If they have a ground type, I can use Garchomp as an alternative lead and set up stealth rocks to wear the opponents down as they switch in and let my other teammates sweep. Rockium Z is good for Zapdos, Dragonite, Charizard Mega-Y, Moltres, and Volcarona. Rough Skin can punish Knock off after the Z-move has been used. Tera Steel is for any fairies trying to wear Garchomp down. Tera Fire is good too, since it won't be predictable.
Iron Valiant @ Choice Specs
Ability: Quark Drive
Nature: Timid, Tera Type: Fairy
EVS: 4 DEF, 252 SPA, 252 SPE.
Aura Sphere
Moonblast
Thunderbolt
Psyshock
Iron Valiant is another sweeper which doesn't need to set up to get wincons. With quark drive Speed, it can out speed most non-scarf users. life orb might be better, because of no locking of moves, but specs is more powerful. Thunderbolt to deal with bulky waters such as Toxapex and Alomomola. It can deal with flying types well with thunderbolt, but not Zapdos. If I need to switch out, I can have Gyarados switch in, either mega or non-mega. Psyshock can defeat special walls, such as Clodsire and Galar-Slowking.
Mega-Gyarados @ Gyaradosite
Ability: Mold Breaker
Tera Type: Water (don't need to tera if I'm going mega)
Nature: Jolly
Evs: 252 ATK, 252 SPE, 4 SPD
Earthquake/Substitute
Dragon Dance
Waterfall
Crunch
Mega-Gyarados. A classic. It can set up with dragon dance under dual screens/substitute, which can really pressure the opponent. Its already pretty bulky, so even without investment, it can survive a few hits. Garchomp can switch into electric attacks that threaten Gyarados, but can't stand up against fairies, if Gyarados already mega evolved. Iron moth and Kartana deal with these checks. it can choose between earthquake, or substitute. Earthquake is coverage, and Substitute can block status, like leech seed and toxic. Plus, it can cripple physical attackers with intimidate before mega evolving.
Kartana @ Choice Scarf
Ability: Beast boost
Nature: Jolly. Tera type: Grass
EVS: 252 ATK 252 SPD 4 SPD
Knock Off
Sacred Sword
Smart Strike
Leaf Blade
Kartana serves as a late game cleaner, and a revenge killer. with its MASSIVE 181 attack stat, it can KO anything that isn't invested in defense. With beast boost serving as a semi-Moxie, it can sweep as long as nothing resists its locked move. Knock off can cripple leftovers Pokémon, and heavy-duty boots users, like iron moth, volcarona, and the birds. At a cost. Kartana will most likely be KO'D after they get the item off, due to its very low Special Defense.
Iron Moth @ Heavy Duty Boots
Tera Type: Grass
Ability: Quark Drive
Nature: Timid
EVS: 252 SPA, 4 SPD, 252 SPE
Energy Ball
Sludge Wave
Psychic
Fire Blast
Iron moth benefits from the electric terrain from Tapu Koko a lot. With its already super high SPA, it can ko most threats, after a quark drive boost to SPA. Heavy-duty boots are MANDATORY since it is weak to stealth rock, and spikes. Tera grass energy ball can Suprise threats such as Landorus-T's Earthquake, Water types, and strike back with super effective hits.
If I need to change anything, feel free to tell me. If not, See you!